PROJECT SUMMARY/ABSTRACT Carbohydrates (also known as saccharides or glycans) occupy a central role among biomolecules due to their participation in a number of signaling and recognition processes in biology. Moreover, carbohydrates are essential structural components of numerous vaccines, anti-diabetic and anti-viral drugs, and anti-tumor drug candidates. Despite significant advances in chemical glycosylation methods, general technologies which offer a precise control of anomeric configuration of the glycosidic bond are in demand. In this proposal we aim to develop methods and strategies for efficient and practical synthesis of bioactive oligosaccharides. In Aim 1, we will expand the toolset of nucleophilic glycosyl donors. In Aim 2, we will develop and apply oxidative glycosylation method for the preparation of oligosaccharides with defined anomeric configuration. This novel method will establish a robust protocol for which the configuration of the anomeric bond is pre-defined in the configuration of nucleophilic glycosyl donor and is independent from the structure of the carbohydrate chain, protective groups, and alcohol acceptors. This method, in combination with C-glycosylation, will address the critical challenges of oligosaccharides synthesis and can be incorporated into automated and high-throughput synthesis. Given the generality and a predictable nature of the glycosylation step, this new technology can be used by researchers with minimal training in organic synthesis, and the discoveries of this study can have important impact on the development of new diagnostic tools and therapies.